1. Field of the Invention
The present invention relates to a device for varying the compression ratio of an internal combustion engine and a method for using such a device and in particular relates to a device that can change the compression ratio of this engine by modifying the dead volume of the combustion chamber at the piston top dead center.
2. Description of the Prior Art
EP Patent 0,297,904 discloses a device for varying the compression ratio of an engine wherein the engine includes a crankshaft, a cylinder in which a piston slides in an alternating translational movement by means of a connecting rod connected to the piston and to the crankshaft. The piston defines with the top of the cylinder a combustion chamber including a dead volume at the top dead center (TDC). A rotary eccentric, of the pull type, is disposed between the connecting rod and the piston. The eccentric, in a first position, enables the piston to reduce the dead volume of the combustion chamber while increasing the compression ratio and increases this dead volume in the second position to achieve a lower compression ratio. The eccentric has a groove which cooperates with two locking pins each disposed symmetrically relative to the piston axis enabling the eccentric to be immobilized in one or other of the two positions.
This device, although satisfactory, nonetheless has a number of drawbacks.
One of the drawbacks of such a device resides essentially in the lack of flexibility in the options for adjusting the compression ratio, with only two options for varying the ratio.
Moreover, such a device requires a precise fit between the groove and the pin to prevent any locking of the pin in the groove.
In another type of device for varying the compression ratio, described in German Patent DE-A-42 26 361, the eccentric (which is not a pull type eccentric) is an eccentric driven by the cooperation of a toothed sector of the eccentric with an endless screw.
This device has a major drawback in that the endless screw must be driven to control the rotation of this eccentric. This drive takes up a great deal of space and requires high power levels to overcome the inertia of the moving parts and the various frictions.